Grooveshark

What makes Grooveshark special enough that we recommend it over the dozens of other music streaming web apps? Well, the biggest thing is the size of its library. You can find virtually any song on their site, ready to be played instantly, included in a playlist, or added to your personal library. Your library (available with a free account) allows you to select any number of songs from their larger list, which you can then browse through with an iTunes-like interface.